Such as explained by the article “Base stations for mobile telephony (UMTS-FDD) recommendation on measurements”, project from 17 Sep. 2003, published on the Internet site www.environnement-suisse.ch/electrosmog, UMTS technology (for “Universal Mobile Communication System”) is a third generation mobile telephone technology. Each telecommunication operator operates their own UMTS network.
UMTS radiocommunication systems make it possible to transmit data flows that are clearly higher than the radiocommunication systems compliant with the GSM standard (for “Global System for Mobile”). They are as such indicated not only for voice traffic but also for the transmission of digital images or videos.
In a radiocommunication system, each radiocommunication terminal comprises a transmission line in order to be able to transmit information in the radiocommunication network wherein it is provided to operate.
In relation with FIG. 1, a simplified diagram is shown of a conventional transmission line 100 comprising a power amplifier.
The transmission line 100 comprises an analogue/digital converter 101 (hereinafter designated by ADC 101) which transmits a control signal to a transmitter 102. The transmitter 102 generates an information signal (carrying the information to be transmitted in the network) and transmits it to the power amplifier 103 so that the latter amplifies, before transmitting in the network via an antenna (not shown), the information signal. An output 104 of the power amplifier 103 is connected to a calibrating point 105 which makes it possible to measure the output power of the power amplifier 103 during the calibrating of the line 100.
On the control of the power of the amplifier 103 of the transmission line 100, the GSM standard is much less restrictive than the UMTS standard. Indeed, for example, according to the GSM900 standard, the power servo must be carried out in steps of 2 dB with a precision which ranges from +/−2 dB to +/−5 dB according to the power level between each step and this for an output power ranging between 33 dBm and 5 dBm while, according to the UMTS standard, the power servo must be carried out in steps of 1 dB with a precision of +/−0.5 dB between each step and this for an output power ranging between +21 dBm and −50 dBm.
Within the framework of transmission lines compliant with the GSM standard, the power amplifier 103 is conventionally a nonlinear power amplifier that operates in compressed mode. The power level at the output of the transmitter 102 is fixed, it is the only application, by means of the control signal, by the ADC 101 to the amplifier 103, via the transmitter 102, of a power setpoint which makes it possible to directly manage the output power levels of the amplifier 103. In this case, in order to carry out the calibrating, according to the mode for coupling and mode for detecting the output power of the amplifier, it is sufficient to take two to four measuring points.
Among the transmission lines compliant with the UMTS standard (hereinafter called UMTS transmission lines), first UMTS transmission lines use a fixed-gain amplifier. These amplifiers are more linear than the amplifiers of GSM transmission lines as they are specifically polarised for this single gain. Such transmission lines require only a few calibrating points, simple linear or polynomial sections obtained using a few measuring points is sufficient for carrying out the calibrating of the transmission line and as such comply with the UMTS standard.
However, second transmission lines compliant with the UMTS standard use a double-gain amplifier: which can be configured in such a way as to have a low gain or configured in such a way as to have a high gain.
The calibrating of these second transmission lines is complex due to the restrictions imposed by the UMTS standard in particular in terms of precision on the step of the power servo of the amplifier and the fact that the amplifier is a double-gain amplifier.
The application of the conventional techniques for calibrating first UMTS lines by section of the polynomial or linear type with these second UMTS lines does not procure enough precision in particular on switching from the low gain configuration to the high gain configuration (or inversely) of the amplifier. Moreover, these conventional techniques are not very robust with regards to the gain dispersion of the transmission line.